1. Field of the Invention
The present invention relates to an oil-impregnated bearing and rotor shaft combination that includes an oil-impregnated bearing mounted in an axle tube in a slip-fit manner for pivotally holding the rotor shaft and for preventing leakage of lubrication oil.
2. Description of the Related Art
A typical conventional heat-dissipating fan or brushless motor includes a rotor having a shaft pivotally held by a bearing. Commonly used bearings include ball bearings or oil-impregnated bearings (self-lubricating bearings). An oil-impregnated bearing is generally tightly secured to an inner periphery of an axle tube or bearing seat for pivotally holding the rotor shaft. It is, however, found that the oil-impregnated bearing is compressed in the radial direction and thus results in deformation in an inner periphery of a hole in the oil-impregnated bearing. As a result, non-smooth friction occurs between the rotor shaft and the inner periphery defining the hole of the oil-impregnated bearing. Although such deformation is relatively small, rotational noise tends to occur under continuous operation of the rotor shaft at high speed. In addition, a gap between the rotor shaft and the inner periphery defining the hole of the oil-impregnated bearing becomes larger due to continuous non-smooth friction. Vibrations occur during rotation of the rotor shaft and greater noise is generated. The operating life of the bearing is accordingly shortened.
U.S. Pat. No. 5,610,462 to Takahashi issued on Mar. 11, 1997 discloses a brushless motor in which an oil-impregnated sleeve bearing is inserted in a bearing holder having a cylindrical shape with a closed bottom, and a rotating shaft is inserted in the oil-impregnated sleeve bearing in such a manner that the rotating shaft may freely rotate. Nevertheless, some of the elements are difficult to manufacture, such as the boss 58 and the cut-away portions 46 d1 of the rotor, as the boss and the cut-away portions must mate with each other precisely in order to prevent oil leakage and to provide easy assembly procedure.
It is a primary object of the present invention to provide an oil-impregnated bearing and rotor shaft combination in which the elements can be manufactured and obtained easily and leakage of lubrication oil is prevented and rotational noise is reduced.
It is another object of the present invention to provide an oil-impregnated bearing and rotor shaft combination in which the oil-impregnated bearing mounted in an axle tube in a slip-fit manner for avoiding deformation of an inner periphery of the hole of the oil-impregnated bearing and for pivotally holding the rotor shaft in a smooth maimer.
It is a further object of the present invention to provide an oil-impregnated bearing and rotor shaft combination that may prevent leakage of lubrication oil and lengthen operating life of the bearing.
In accordance with the present invention, an upper cap is tightly and securely mounted to an upper end of the axle tube. After a shaft of a rotor is extended through an opening in the upper cap, a retainer, e.g., a retainer ring, is provided to retain the rotor shaft in place. An oil-impregnated bearing is mounted around the rotor shaft in a slip-fit manner in a position below the retainer. A lower cap seals the lower end of the axle tube for pivotally supporting the rotor shaft and the oil-impregnated bearing is restrained between the upper and lower caps.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.